Pumping of the human heart is caused by precisely timed cycles of compartmental contractions of the heart muscle which lead to an efficient movement of blood into the heart and out to the various bodily organs. These precisely timed cycles are controlled and directed by electrical signals that are conducted through the cardiac tissue and can be referred to as pacing signals.
The sinoatrial node (SA node) is the heart's natural pacemaker, located in the upper wall of the right atrium. The SA node spontaneously contracts and generates nerve impulses that travel throughout the heart wall causing both the left and right atriums to sequentially contract according to a normal rhythm for pumping of the heart. These electrical impulses continue to the atrioventricular node (AV node) and down a group of specialized fibers called the His-Purkinje system to the ventricles. This electrical pathway must be exactly followed for proper functioning of the heart.
When the normal sequence of electrical impulses changes or is disrupted, the heart rhythm often becomes abnormal. This condition is generally referred to as an arrhythmia and can take the form of such arrhythmias as tachycardias (abnormally fast heart rate), bradycardias (abnormally slow heart rate) and fibrillations (irregular heart beats).
Of these abnormal heart rhythms, fibrillations, and particularly atrial fibrillations, are gaining more and more attention by clinicians and health workers. Atrial fibrillation develops when a disturbance in the electrical signals causes the two upper atrial chambers of the heart to quiver instead of pump properly. When this happens, the heart is unable to discharge all of the blood from the heart's chambers thus creating a situation where the blood may begin to pool and even clot inside the atrium. Such clotting can be very serious insofar as the clot can break away from the atrial chamber and block an artery in the brain, and thereby cause a stroke in the individual.
A variety of treatments have been developed over the years to treat atrial fibrillation, namely, treatments to either mitigate or eliminate electrical conduction pathways that lead to the arrhythmia. Those treatments include medication, electrical stimulation, surgical procedures and ablation techniques. In this regard, typical pharmacological treatments have been previously disclosed in U.S. Pat. No. 4,673,563 to Berne et al.; U.S. Pat. No. 4,569,801 to Molloy et al.; and also by Hindricks, et al. in “Current Management of Arrhythmias” (1991), the contents of which are herein incorporated by reference.
Surgical procedures, such as the “maze procedure”, have also been proposed as alternative treatment methods. The “maze” procedure attempts to relieve atrial arrhythmia by restoring effective atrial systole and sinus node control through a series of incisions.
The Maze procedure is an open heart surgical procedure in which incisions are made in both the left and right atrial walls which surround the pulmonary vein ostia and which leave a “maze-like” pathway between the sinoatrial node and the atrioventricular node. The incisions are sewn back together but result in a scar line which acts as a barrier to electrical conduction.
Although the “maze” procedure has its advantages, in practice it can be a complicated and a particularly risky procedure to perform since the surgeon is making numerous physical incisions in the heart tissue. Due in part to the risky nature of the Maze procedure, alternative, catheter-based treatments have been advanced. Many of these catheter devices create the desired electrical block by way of ablation devices designed to burn lesions into the target tissue. Examples of these devices can be seen in U.S. Pat. No. 6,254,599 to Lesh; U.S. Pat. No. 5,617,854 to Munsif; U.S. Pat. No. 4,898,591 to Jang et al.; U.S. Pat. No. 5,487,385 to Avitall; and U.S. Pat. No. 5,582,609 to Swanson, all incorporated herein by reference.
Although ablation catheter procedures remain less invasive than previous surgical methods like the “maze” procedure, they nevertheless retain a significant element of risk. For example, ablation procedures often utilize high power RF energy or ultrasonic energy, which may adequately create electrical block, but their inherent destructive nature allows for the possibility of unintended damage to the target tissue or nearby areas.
Further, it is often difficult to achieve certainty as to whether the appropriate amount of ablation has been performed uniformly around the perimeter of the target site or if the desired site is even being ablated.
Ablation procedures have also seen an occurrence of stenosis in the pulmonary veins as a response to the ablation. This is a serious complication and as a result, many doctors try to limit their treatment to the ostium of the pulmonary veins to minimize the risk of creating a stenosis in the pulmonary veins.
Finally, various implant devices have also been proposed. Examples of such proposed devices are disclosed in co-pending U.S. application Ser. No. 10/192,402 filed Jul. 8, 2002 entitled Anti-Arrhythmia Devices and Methods of Use, the entire contents of which is hereby incorporated by reference.
The solutions in the prior art, however, are not believed to be entirely effective in many cases, and indeed may result in actually inducing long term arrhythmias and inefficacy.
As a result, what is needed are minimally invasive techniques for creating electrical block in the pulmonary veins which reduce the complication risk of previously known procedures, while increasing effectiveness and speed of the procedure to create electrical block.